Appendix A
Emerging and Reemerging Waterborne Pathogens

This appendix addresses a requirement of the committee’s statement of task; specifically the requirement to “. . . define currently known waterborne pathogen classes and anticipate those emerging waterborne pathogens that are likely to be of public health concern.” For the purposes of this report, emerging and reemerging pathogens can be defined as recently identified waterborne pathogens or those pathogens that were once thought to be under control from a public health perspective but are reappearing and causing increased incidence or geographic range of infections in exposed human populations. In recent years, several such waterborne pathogens have arisen, including recognized pathogens from fecal sources and some “new” pathogens from environmental sources. Several factors contribute to the (re)emergence of waterborne pathogens in the United States (Theron and Cloete, 2002), including the following:

Changes in human demographics. There is an increasing number of “vulnerable subpopulations” in the United States such as infants, children, pregnant women, the elderly, and the immunocompromised (e.g., AIDS patients) who are particularly susceptible to infections resulting from exposure to waterborne pathogens compared to the general populace (see also NRC, 2001).

Changes in human behavior. Urbanization of rural areas allows infections arising in formerly isolated areas, which may once have remained obscure and localized, to reach large and densely populated areas. The use of heated drinking water with warm water reservoirs also promotes the emergence of waterborne pathogens because these systems are ideal habitats for a number of pathogens of public health concern, such as Legionella spp. (Lee and West, 1991).

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Indicators for Waterborne Pathogens
Appendix A
Emerging and Reemerging Waterborne Pathogens
This appendix addresses a requirement of the committee’s statement of task; specifically the requirement to “. . . define currently known waterborne pathogen classes and anticipate those emerging waterborne pathogens that are likely to be of public health concern.” For the purposes of this report, emerging and reemerging pathogens can be defined as recently identified waterborne pathogens or those pathogens that were once thought to be under control from a public health perspective but are reappearing and causing increased incidence or geographic range of infections in exposed human populations. In recent years, several such waterborne pathogens have arisen, including recognized pathogens from fecal sources and some “new” pathogens from environmental sources. Several factors contribute to the (re)emergence of waterborne pathogens in the United States (Theron and Cloete, 2002), including the following:
Changes in human demographics. There is an increasing number of “vulnerable subpopulations” in the United States such as infants, children, pregnant women, the elderly, and the immunocompromised (e.g., AIDS patients) who are particularly susceptible to infections resulting from exposure to waterborne pathogens compared to the general populace (see also NRC, 2001).
Changes in human behavior. Urbanization of rural areas allows infections arising in formerly isolated areas, which may once have remained obscure and localized, to reach large and densely populated areas. The use of heated drinking water with warm water reservoirs also promotes the emergence of waterborne pathogens because these systems are ideal habitats for a number of pathogens of public health concern, such as Legionella spp. (Lee and West, 1991).

OCR for page 267
Indicators for Waterborne Pathogens
Breakdown of public health systems. Although public health measures such as water and wastewater treatment act to minimize human exposure to waterborne pathogens and reduce the incidence of waterborne disease, these systems can and do fail on occasion—often with extensive public health ramifications. Such breakdowns also provide opportunities for pathogens to reemerge.
Microbial adaptation. Microbes are constantly evolving in response to changing environments and environmental conditions. With the increasing use and release of antibiotics and drugs into our waterways, strains of microorganisms that are antibiotic- or drug-resistant have also been increasingly identified (see Chapter 3 for further information).
Changes in agricultural practices. Intensive farming operations (especially concentrated/confined animal feeding operations, or CAFOs) result in high concentrations of animal wastes, which in turn lead to increased pollution of our nation’s waters by runoff and intentional (point source) discharges. This is of public health concern because a number of pathogens (e.g., Cryptosporidium) routinely contained in such fecal sources can be transmitted to humans through inadequately treated drinking water or through recreational water exposure.
Throughout this report, waterborne pathogens (including those that can be considered emerging or reemerging) can be categorized into four groups: viruses, bacteria, protozoa, and others. (“Others” include cyanobacterial toxins and protists; however, this group is not discussed extensively in this report for reasons outlined in Chapter 1.) Indeed, Chapter 3 on the ecology and evolution of waterborne pathogens and indicator organisms is divided into separate sections for viruses, bacteria, and protozoa. The issue of new and (re)emerging waterborne pathogens has been reviewed in several published reports and articles (EPA, 1998; LeChevallier et al., 1999; Szewzyk et al., 2000; Theron and Cloete, 2002) from a public health and/or water treatment perspective. Therefore, in response to the statement of task, this appendix includes a brief summary of the health effects and mode of transmission of select emerging and reemerging waterborne pathogens in all four groups taken from these and other sources (see Table A-1). Lastly, several of the waterborne pathogens listed in Table A-1 are discussed to some extent (in some cases extensively) elsewhere in this report.
REFERENCES
EPA (U.S. Environmental Protection Agency). 1998. Announcement of the Drinking Water Contaminant Candidate List; Notice. Federal Register 61(94): 24354-24388.
Hilton, C., K. Holmes, K. Spears, L.P. Mansfield, A. Hargreaves, and S.J. Forsythe. 2000. Arcobacter, newly emerging food and waterborne pathogens. Presentation at SGM Warwick, April 12.
LeChevallier, M.W., M. Abbaszdegan, A.K. Camper, G. Izaguirre, M. Stewart, D. Naumovitz, M. Mardhall, C.R. Sterling, P. Payment, E.W. Rice, C.J. Hurst, S. Schaub, T.R. Slifko, J.B. Rose, H.V. Smith, and D.B. Smith. 1999. Emerging pathogens: Names to know and bugs to watch out for. Journal of the American Water Works Association 91(9): 136-172.

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